Bacterial actin: architecture of the ParMRC plasmid DNA partitioning complex

EMBO J. 2008 Aug 20;27(16):2230-8. doi: 10.1038/emboj.2008.152. Epub 2008 Jul 24.


The R1 plasmid employs ATP-driven polymerisation of the actin-like protein ParM to move newly replicated DNA to opposite poles of a bacterial cell. This process is essential for ensuring accurate segregation of the low-copy number plasmid and is the best characterised example of DNA partitioning in prokaryotes. In vivo, ParM only forms long filaments when capped at both ends by attachment to a centromere-like region parC, through a small DNA-binding protein ParR. Here, we present biochemical and electron microscopy data leading to a model for the mechanism by which ParR-parC complexes bind and stabilise elongating ParM filaments. We propose that the open ring formed by oligomeric ParR dimers with parC DNA wrapped around acts as a rigid clamp, which holds the end of elongating ParM filaments while allowing entry of new ATP-bound monomers. We propose a processive mechanism by which cycles of ATP hydrolysis in polymerising ParM drives movement of ParR-bound parC DNA. Importantly, our model predicts that each pair of plasmids will be driven apart in the cell by just a single double helical ParM filament.

MeSH terms

  • Actins / chemistry
  • Actins / metabolism*
  • Actins / ultrastructure
  • DNA Topoisomerase IV / chemistry
  • DNA Topoisomerase IV / genetics
  • DNA Topoisomerase IV / metabolism
  • DNA Topoisomerase IV / ultrastructure
  • DNA, Bacterial / metabolism*
  • DNA, Bacterial / ultrastructure
  • Escherichia coli Proteins / chemistry
  • Escherichia coli Proteins / metabolism*
  • Escherichia coli Proteins / ultrastructure
  • Models, Molecular
  • Peptides / chemistry
  • Plasmids / metabolism*
  • Promoter Regions, Genetic / genetics
  • Protein Binding
  • Protein Structure, Secondary


  • Actins
  • DNA, Bacterial
  • Escherichia coli Proteins
  • ParM protein, E coli
  • ParR protein, E coli
  • Peptides
  • DNA Topoisomerase IV